Final answer:
Musical instruments are grouped by how they produce sound, with smaller instruments generating higher-pitched sounds due to shorter wavelengths and larger instruments producing lower pitches because of longer wavelengths.
Step-by-step explanation:
Musical instruments are grouped by how they produce sound or pitch. The pitch of a sound corresponds to its frequency, and the size of the instrument directly affects this. Smaller instruments, like a piccolo, produce higher-pitched sounds because they generate shorter wavelengths and thus higher frequencies. Conversely, larger instruments, such as a tuba, produce lower-pitched sounds, which have longer wavelengths and lower frequencies. For example, a guitar would be classified based on the fact that it produces sound through the vibration of strings, making it a string instrument.